MCP4250, a novel chemoreceptor, mediates chemotaxis toward halogenated nitrophenols in Cupriavidus sp. CNP-8

Bacterial chemotaxis toward synthetic halo- and nitro-substituted aromatic compounds has been observed; however, the molecular mechanisms by which bacteria sense these pollutants remain unclear. Cupriavidus sp. CNP-8 is capable of utilizing a range of halogenated nitroaromatic compounds for growth. In this study, we demonstrated the chemotactic responses of strain CNP-8 to several halogenated nitrophenols. Genetic deletion and complementation experiments revealed that MCP4250, a methyl-accepting chemotaxis protein (MCP), is involved in bacterial chemotaxis toward monohalogenated and dihalogenated nitrophenols. Isothermal titration calorimetry (ITC) analyses indicated that the ligand-binding domain of MCP4250 (MCP4250LBD) did not bind to halogenated nitrophenols, but did bind to cis-aconitate, citrate, malate, isocitrate, and α-ketoglutarate, with cis-aconitate as the tightest-binding ligand. This suggests that MCP4250 triggers chemotaxis toward halogenated nitrophenols by sensing TCA cycle intermediates. Genetic deletion of the LBD fragment of mcp4250 gene indicated that MCP4250LBD plays an important role in chemotactic responses. Furthermore, the key amino acid residues within a putative LBD pocket were characterized by site-directed mutagenesis and ITC assays. Phylogenetic analysis suggests that MCP4250 has a unique evolutionary origin distinct from other functionally characterized chemoreceptors. To date, MCP4250 is the first biochemically identified chemoreceptor that mediates chemotaxis toward halogenated nitroaromatic compounds, extending our understanding of chemoreceptor diversity, as well as providing an example of how bacteria may sense xenobiotic pollutants through metabolic integration rather than direct substrate-receptor interactions. Key points MCP4250 is the first chemoreceptor involved in bacterial chemotaxis toward halogenated nitrophenols. MCP4250 triggers chemotaxis toward halogenated nitrophenols by sensing TCA cycle intermediates. MCP4250 has a unique evolutionary origin distinct from other functionally characterized chemoreceptors.